This invention relates to output level detectors and in particular to devices for sensing and indicating the voltage level of a battery.
Examples of devices for indicating the voltage level or charge/discharge status of a battery abound on the art. Generally they fall into two general types of structures.
The one type is that which is purposely kept simple, generally so much so that any kind of activity of the indicator is kept to a minimum. That is, there is no flashing, color change or other indication to give early warning of low battery charge level. If any is provided at all, it is by sequentially activating a number of discrete indicators such as light emitting diodes. An example of this type is Lohrmann, U.S. Pat. No. 4,027,231. Cowles, et al, U.S. Pat. No. 4,318,092, relies upon a gauge-based indicator. Lang, U.S. Pat. No. 4,758,772 and Huber et al., U.S. Pat. No. 4,338,596, both include oscillators which are activated to cause flashing of indicators only upon the sensing of insufficient voltage in the battery.
The other type provides a much higher level of functionality, and these devices can be so complex as to be more expensive than those in the first category, because they include logic circuits and even microprocessors. Examples of this second type are Kageyama et al, U.S. Pat. No. 4,521,735, which discloses the use of a microprocessor; Ijntema, U.S. Pat. No. 4,536,757, including a number of logic circuits; Kong, U.S. Pat. No. 4,714,877, disclosing a circuit employing over 30 transistors; and Randin et al., U.S. Pat. No. 4,743,855.
What is needed is a simple and inexpensive circuit, the power requirements of which are low, and which gives a linear indication of impending battery discharge. This invention relates to improvements to some of the devices described above and to solutions to some of the problems raised or not solved thereby.